Process of producing cellulosic pulp



Patented Feb. 16, 1932 UNITED STATES PATENT! OFFICE" ELTON R. DARLING, OF'DANVILLE, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO OF NEW YORK, N. Y., A CORPORATION OF GORNSTALK PRODUCTS COMPANY, INC.,

DELAWARE PROCESS OF PRODUCING GELL'ULOSIO PULP No Drawing.

The present invention relates tothe production of a superior form of paper from vegetable plants of annual growth, such,for

example, as are exemplified by the corn (maize) plant, and from similar agricultural waste products.

In its broadest aspects the invention contemplates the use of all cell-ulosic agricultural waste, and specifically concerns the process applicable to the conversion of corntalks into paper pulp by a novel and economical process.

One of the objects of the invention is to enable the production of a high grade cellulose pulp from, for example, cornstalks by a method of treating said stalks with an alkaline solution, as, for example, caustic soda; the operationbeing so conducted that the free alkali strength of the solution is maintained substantially constant during the digestion whereby superior results, as compared with the old and known methods, are obtained.

The agricultural waste contemplated to be used for carrying out the present invention is usually obtained from annual plants, in which the fiber has had a life and growth of but a few months and, therefore, from both a physical as well as a chemical standpoint, mustvbe treated less drastically than in the processes usually employed for making paper.

In the manufacture of cornstalk vpulp,it is necessary to digest the cornstalks with a dilute alkaline solution.

The practice heretofore consisted in treating the agricultural wastes in a digestor with a caustic soda solution of a strength suflicient to clean and separate the fiber but not strong enough to work any injury thereto. As the digestion proceeded I discovered under actual working conditions, that in the first fifteen minutes after pressure in the digestor had developed, twenty per cent. of the caustic soda in the digestion liquor had been converted into sodium carbonate and sodium salts of complex organic bodies, and at the end of the first hour of the digestion, fortyeight per cent. of the caustic soda had been' Application filed December 13, 1928. Serial No. 325,894.

upon the fiber would be unduly drastic and therefore undesir ble, and one of the objects of this new met od is to provide a means whereby the cooking liquor has, at the start of the operation, a caustic soda strength not greater than that of the cooking liquor used in former. methods at any stage, but which said strength is maintained and not allowed to decrease, by periodically passing into the digestor by slow feed through a pumping and circulating system, a solution of caustic soda of such quantity and strength that when it has thoroughly commingled with the total amount of digestion liquor in the digestor, the caustic soda strength will have been restored to its original strength.

In other words, what I aim to accomplish is to keep substantially constant, from start to finish of the digestion operation, the actual free caustic soda content of the liquor circulating through the fibers undergoing treatment. The desired strength of this free caustic soda is equivalent to substantially a one per cent. solution of caustic soda (NaOH). In other words, I commence my operation with a solution containing one per cent. of free NaOH. As the digestion progresses and the caustic soda is used up in carrying out its function, in the process, I introduce into the digestion apparatus, at any suitable point, a solution of caustic soda of about forty per cent. strength in such graduated quantities that the free caustic soda content of the liquor in the digestor will therebybe brought back to and maintained at the desired percentage of approximately one per cent. NaOH. This injection of freshconcentrated caustic soda solution is repeated, at intervals during the process, so that when the process is completed there will still be one per cent. free caustic soda in the liquor. Extensive experimentation and the practice of this process has disclosed the fact that it is possible to plot a curve whereby the progressive destruction of caustic soda in the digestion liquorcan be recorded and that the said curve, having once been established, might be used in controlling the time of addition and the amount of the concentrated caustic solution required to be added during the cooking of each batch of cellulosic material. Also, such a curve provides an excellent means for checking the operations as they progress.

It was further shown that this method of digestion, in which the free caustic strength of the solution is maintained substantially constant throughout the operation, enables a reduction in the digestiontime of approximately twenty-five per cent, and allows the pressure at which the cooking would ordinarily be carried out to be reduced to substantially one-half of that usually employed in the processes as heretofore practiced.

For example, in boiling comminuted cornstalks to obtain paper pulp stock therefrom and working with a concentration of caustic soda as above indicated and at a pressure of about two and one-half atmospheres,

which corresponds roughly to 137 0., of the boiling liquor, from one to one and one-half hours will be sufficient to liberate the cellulose and to solubilize the pentosans, lignins, and other analogous materials in the comstalk substance. k

After the digestion is efiected, the further steps differ in no way from those usually carried out. a

While I have described my-invention in connection with an alkaline digestion, it is obvious that the same is applicable with equal force and efli'ect to digestions where other than alkaline reagents are employed, for example, in digesting with calcium bisulphite the strength of the solution with the digestion is carried out may likewise be maintained constant during the operation by the periodic addition of fresh bisulphite solution. Also, as shown in a joint application of John E. Jackson and myself, Serial No. 280,646, filed May 25, 1928,. where there is described the use of sodium hydroxide and sodium sulphite, the periodic introduction of the said two reagents during the digesting operation may be carried out.

The essential feature of my invention lies in the fortification of the digestion liquor periodically during the progress of the digestion. Obvious modifications in the meth 0d of introducing the caustic soda, such, for example, as introducing the same in the solid form or the introduction of the same in more dilute form than I have shown are to be construed as within the spirit and scope of my invention.

When the digestion set forth above is complete the contents of the digestor are passed to a continuous centrifuge in Which'the liquor and solid portions of the mass are separated.

The solid portions or pulp are ready for' bleaching in any of the known processes, and the liquor is pumped to a receiving tank. The said liquor, because of the way in which it has been treated, may be sent again into process as its caustic soda strength is subinjector that draws its supply from a storage tank of strong reagent, or a suitable pump may be used. Any mechanical expedient capable of effecting the refortification of the solution may be used, as my invention is not to be construed as having apparatus limitations, but is to be interpreted only in accordance with the claims hereunto appended.

I claim:

1. In the process for the alkaline digestion of cellulosic materials the step which comprises fortifying the, digestion liquor during the progress of the digestion, whereby the initial alkali strength of the solution is maintained substantially constant by the periodic addition of fresh additional concentrated alkali solution during the digestion operation.

2. The process of digesting cellulosic materials with an alkaline fiber-liberating reagent which comprises maintaining the initial strength of the alkaline reagent by periodic addition of concentrated alkaline reagent during-the progress of the digestion.

3. The process of liberating fiber from cellulosic material by digestion which comprises treating cellulosic material with an aqueous solution of an alkaline reagent, and maintaining the strength of said solution during the digestion by periodic additions of reagent thereto.

4. The process of liberating fiber from cellulosic material by digestion which comprises treating cellulosic material with an aqueous solution of caustic soda and maintaining the initial strength of said caustic soda solution by periodic additions of fresh caustic sodathereto during the progress of the digestion' 5. The process of liberating fiber from cellulosic material which comprises digesting the same with a relatively weak alkaline solution while maintaining said solution at substantially its initial alkali strength by periodic addition of fresh alkali materials thereto.

6. The process of liberatin fiber from cellulosic-material which comprises digesting the same with a relatively weak alkaline solution while maintaining said solution at substantially its initial alkali strength by periodic addition of strong alkali solution thereto.

7. The process of liberating fiber from cellulosic material which comprises digesting the same with a relatively weak caustic soda solution, while maintaining the initial strength of said solution by periodic addition of fresh caustic soda thereto.

8. The process of liberating fiber from cellulosic material which comprises digesting the same with a relatively weak caustic soda solution; while maintaining the initial strength of said solution by periodic addition of further caustic soda solution thereto.

9. In the process of preparing cellulosic pulp from plants of annual growth, such as cornstalks, the step which comprises treating said plants with a substantially one per cent. caustic soda solution while maintaining the solutionat substantially the said strength during the digestion by addition of caustic soda thereto.

10. In the process of preparing cellulosic pulp from plants of annual growth, such as cornstalks, the step which comprises treating said plants with a substantially one per cent. caustic soda solution while maintaining the solution at substantially the said strength during the digestion by addition of caustic soda solution thereto.

In witness whereof, I have hereunto subscribed my name.

ELTON R. DARLING. 

